When people attempt to perform two simple sensorimotor tasks close together in time, performance deteriorates. Detailed chronometric analysis of this dual-task inerference can provide powerful empirical constraints on theodes of the mechanisms that carry out perceptual, cognitive and response processes. in previous work, the Pi has found converging evidence for a theory of dual-task interference that postulates two distinct components. When complex visual stimuli are presented at the same time, perceptual processing proceeds simultaneously, with impairments in accuracy dependent upon complexity. When response selection is required on one task, however, response selection on another task must wait: this processing stage is subject to discrete queueing. The work proposed here will address four questions, to test, elaborate and extend this theory. First, perceptual interference will be examined in auditory discrmination tasks (combined with other auditory or visual tasks), to determine whether perceptual interference reflects separate pools of resources tied to particular sensory modalities. Second, several different methods will be employed to determine whether post-perceptual processes other than response selection are subject to discrete queueing; this work will focus on semantic categorization and shifts of visual attention. Third, the possibility of independent control of different response modalities will be examined, focussing on the case of oculomotor control (saccadic and smooth pursuit eye movements). Pilot data suggests a surprising degree of independence in certain oculomotor tasks. Finally, we will investigate how extensive practice reduces dual-task interference. Previous work has suggested that well-practiced tasks may become completely "automatized", but the evidence is open to various interpretations; chronometric methods will be used to determine exactly which components of interference are affected by practice, and how they are affected.